The present invention relates to the elimination of polluting components, or of solid, liquid or gaseous impurities, from the exhaust gasses of an internal combustion engine.
A particular, but not exclusive, application is the purification of the exhaust gasses of a diesel engine.
Very many methods and devices for filtering internal combustion engine exhaust gasses have been proposed in the past.
In particular, there is known from the document GB-A-923 431, a method of eliminating solid, liquid and gaseous impurities from a flow of hot gasses in which the latter are conveyed and which comprises steps consisting of adding cool and clean air to the gasses in such a quantity and in such conditions that the flow of gasses is cooled down to a temperature below the point of condensation of that component from among the gaseous impurities that has the lowest boiling point, which means that the individual components forming the gaseous impurities condense successively and form droplets which are deposited on the liquid and solid impurities which are also contained in the flow of gas thus forming larger-sized particles. The liquid and solid particles thus obtained are then separated from the flow of gasses in a separating chamber.
In an application to an internal combustion engine, before the addition of the flow of cool and clean air, the flow of hot gasses is previously circulated in a heat exchanger in order to cool it and the separating chamber consists of an electro-filter.
There is also known, from the document EP-A-0 346 803, a method for continuously eliminating the soot and condensable volatile components from the exhaust gasses of a diesel engine, in which the hot exhaust gasses from the diesel engine are made to pass alternately through two heat exchangers, the soot and the condensable volatile components of the gasses being partially deposited on the surfaces of the heat exchanger. The exhaust gasses, cooled and charged with the remainder of the soot and of the condensable components, then pass into a coarse particles separator or a ceramic filter and then, in one of the embodiments of the invention, through an electrostatic separating device. When one of the heat exchangers is partially or totally clogged by the soot and the condensable volatile components, the latter is heated up and cleaned by combustion whilst the purification of the hot gasses takes place by passing through the other heat exchanger.
Such filtering methods and devices are relatively complex and are therefore expensive and not very easy to implement.
The present invention aims to overcome these disadvantages.
In particular, the invention proposes a filtering technology which is simple and easy to implement, whilst being at least as efficient as the existing technologies. It also proposes a filtering device which is compact and adaptable to any motor vehicle.
In order to do this it proposes, in a general manner, a device for filtering internal combustion engine exhaust gasses, comprising an electrostatic filtering chamber equipped with electrostatic filtering means, a line for supplying exhaust gasses into the filtering chamber, in fluid communication with an inlet of the filtering chamber, at one of the ends of the supply line, the other end of the supply line being provided with an opening whose inlet orifice is adapted to allow the penetration of the exhaust gasses and of a flow of ambient air intended for lowering the temperature of the exhaust gasses, characterised in that intake means, intended for drawing in the exhaust gasses and the air flow are mounted downstream of an outlet of the filtering chamber and in fluid communication with this outlet, in order to allow the mixture of exhaust gasses and air to pass into the said filtering chamber and to reject the filtered gasses into the environment and in that a filter for coarse solid particles and droplets derived from the mixture is mounted in the filtering chamber, upstream of the electrostatic filtering means.
The combination of a mechanical filter, electrostatic filtering means and the drawing through these things of a mixture of hot exhaust gasses and ambient cooling air makes it possible to filter these exhaust gasses in a particularly efficient and simple manner. Furthermore, the resulting device is compact and easy to use.
More particularly, the intake means make it possible to cause a mixture of hot exhaust gasses an ambient cooling air to penetrate into the supply line and to make this mixture pass into the filtering chamber at a constant flow rate.
Furthermore, the exhaust gasses are efficiently cooled and do not therefore damage the electrostatic filtering means.
Furthermore, the mechanical filter, particularly when the latter is constituted by an impingement-type filter, makes it possible to obtain a substantially constant pressure over the whole of the intake area of the electrostatic filtering means.
Preferably, another filter for solid particles and droplets is mounted downstream of the electrostatic filtering means, in the filtering chamber. Thus, the processing of the exhaust gasses in the electrostatic filtering means takes place in the whole of useful volume of these means, with no dead volume which could result in load loss phenomena.
Also preferably, an active carbon filter is mounted in the filtration chamber, downstream of the said other filter.
In order to prevent back-flow and turbulence phenomena, the opening of the exhaust gasses supply line comprises a conical nozzle whose wall is preferably pierced with holes.
In a preferred embodiment, the filtering means comprise two or more filtering stages.
The present invention also proposes a method of filtering the exhaust gasses of an internal combustion engine consisting in cooling the exhaust gasses by the addition of ambient air; in filtering these exhaust gasses in a filtering chamber equipped with electrostatic filtering means; characterised in that it consists in drawing the exhaust gasses and the ambient air flow through the filtering chamber and in filtering the mixture of exhaust gasses and ambient air by means of a filter for coarse solid particles and droplets, placed upstream of the electrostatic filtering means.
Advantageously, there is also filtered the mixture of exhaust gas and ambient air coming from the electrostatic filtering means, by means of another filter for solid particles and droplets.
Preferably, there is also filtered the mixture of exhaust gasses and ambient air coming from the other filter by means of an active carbon filter.
Finally, the present invention proposes a motor vehicle equipped with a filtering device such as defined above.
The supply line can be connected to the outlet of the exhaust silencer box or directly to the outlet of the exhaust manifold of the internal combustion engine and comprises means adapted to receive the corresponding outlet.
Furthermore, the filtering device can be installed in the boot or in the engine compartment of the vehicle.